1. Field of the Invention
The present invention relates to a method and apparatus for removing particles from surfaces, and avoiding particle accumulation on surfaces during, electrochemical mechanical processing.
2. Description of the Related Art
Conventional semiconductor devices generally include a semiconductor substrate, usually a silicon substrate, and a plurality of sequentially formed dielectric interlayers such as silicon dioxide and conductive paths or interconnects made of conductive materials. The interconnects are usually formed by filling a conductive material in trenches etched into the dielectric interlayers. In an integrated circuit, multiple levels of interconnect networks laterally extend with respect to the substrate surface. The interconnects formed in different layers can be electrically connected using vias or contacts. A conductive material filling process of such features, i.e., via openings, trenches, pads or contacts can be carried out by depositing a conductive material over the substrate including such features.
Copper and copper alloys have recently received considerable attention as interconnect materials because of their superior electromigration and low resistivity characteristics. The preferred method of copper deposition is electrodeposition. During fabrication, copper is deposited on the substrate that has been previously coated with a barrier layer and then a seed layer. The barrier layer coats the vias and the trench as well as the surface of the dielectric layer to ensure good adhesion and acts as a barrier material to prevent diffusion of the copper into the semiconductor devices through the dielectric insulation layer. Typically, seed layer forms a conductive material base for copper film growth during the subsequent copper deposition. Typical barrier materials generally include tungsten, tantalum, titanium, their alloys, and their nitrides. The deposition process can be carried out using a variety of processes. After depositing copper into the features on the semiconductor wafer surface, an etching, an electropolishing (also called electroetching), an electrochemical mechanical etching (ECME) or a chemical mechanical polishing (CMP) step may be employed. These processes remove the conductive materials off the field regions of the surface, thereby leaving the conductive materials only within vias, trenches and other features.
In conventional electrodeposition techniques, copper is coated on the wafer surface in a conformal manner. As shown in FIGS. 1-3, when, for example, a dual damascene structure on the wafer surface is coated with copper using conventional plating, it yields a rather conformal film. FIGS. 1-3 show three possible stages in the conventional process. In a first stage shown in FIG. 1, the dual damascene structure 10 with a wide trench 11, a small via 12 covered with a barrier layer 13 and a copper seed layer 14 is shown. As the copper film is electroplated in a second stage shown in FIG. 2, the copper 15 quickly fills the small via 12 but coats the wide trench and the surface in a conformal manner. When the deposition process is continued, the wide trench is also filled with copper in a third stage shown in FIG. 3, but with a resulting large step ‘S’ and a thick surface copper layer ‘t’. Thick copper on the surface presents a problem during the material removal step such as a CMP step, which is expensive and time consuming. Techniques that can yield thin surface copper overburden and small or no ‘S’ step are very attractive, which is exemplified in FIG. 4.
The importance of overcoming the various deficiencies of the conventional electrodeposition techniques is evidenced by technological developments directed to the deposition of planar copper layers. For example, U.S. Pat. No. 6,176,992, entitled “Method and Apparatus for Electrochemical Mechanical Deposition” and commonly owned by the assignee of the present invention, describes in one aspect an electro chemical mechanical deposition technique (ECMD) that achieves deposition of the conductive material into the cavities on the substrate surface while minimizing deposition on the field regions by polishing the field regions with a pad as the conductive material is deposited, thus yielding planar copper deposits. In another aspect, this application describes an electrochemical mechanical etching (ECME) or electroetching or electropolishing technique that removes conductive material from the surface of a workpiece.
U.S. Pat. No. 6,534,116 for “Plating Method and Apparatus that Creates a Differential Between Additive Disposed on a Top Surface and a Cavity Surface of a Workpiece Using an External Influence,” also assigned to the same assignee as the present invention, describes in one aspect another ECMD method and apparatus for plating a conductive material onto the substrate by creating an external influence, such as causing relative movement between a workpiece and a mask, to cause a differential in additives to exist for a period of time between a top surface and a cavity surface of a workpiece. While the differential is maintained, power is applied between an electrode (in this case anode) and the substrate to cause greater relative plating of the cavity surface than the top surface.
These ECMD methods can deposit metals in and over cavity sections on a workpiece in a planar manner. Some methods even have the capability to provide deposits with excess metal in and over the cavities. In such above-mentioned processes, a pad, a mask or a sweeper, hereinafter collectively referred to as a workpiece-surface-influencing device (WSID), can be used during at least a portion of the electrodeposition process when there may be physical contact between the workpiece surface and the WSID. The physical contact, polishing, or the external influence affects the growth of the metal by effectively reducing the growth rate on the top surface with respect to the features. During the process step that involves the WSID being in close proximity to, and typically in contact with, the metal surface, small particles of the metal may attach onto the WSID material. These particles may exist because of the fact that they may be just physically removed from the substrate surface or they may originate from the plating solution due to poor filtration of the plating solution. In any case once the conductive metal particles attach themselves to a location on the WSID, they may start growing in size because they become cathodic with respect to the electrode. Further, since they are conductive they receive coating and thus grow in size.
ECME methods also use a WSID, and during usage of these methods, the WSID is also in close proximity to, and typically in contact with, the metal surface of the workpiece. During ECME, the potential applied between the workpiece surface and the electrode is reversed rendering the workpiece surface anodic. Therefore, material is removed from the workpiece surface. If WSID is not used during this material removal step, i.e. if there is no mechanical action on the workpiece surface, the process is referred to as just electrochemical etching or polishing. It should be noted that in general both ECMD and ECME processes are referred to as electrochemical mechanical processing (ECMPR) hereinafter, since both involve electrochemical processes and mechanical action.
In addition to conductive particles, there are also non-conductive particles that may accumulate on the WSID material. The non-conductive particles may originate from other parts of the system, such as from the plating solution due to the poor filtration or from the WSID material itself due to the wear and tear during processing.
Presence of such particles on or in close proximity of the surface of the WSID is undesirable because if they become loose and find their way to the interface between the WSID and the workpiece surface, they can cause scratches, inclusions, or other defects on the workpiece surface or they can actually cause scratches on the surface of the WSID, especially if the WSID has a non-flat surface profile.
Therefore, elimination of such particles, or process steps to limit their growth, are very important to increase process yield and the lifetime of the WSID used in planar metal deposition techniques in which particles may come close to or touch the workpiece surface, and particularly when particles are disposed on a WSID that touches the workpiece surface.